When a certain kind of rock called marble is polished it is beautiful. It looks like a shiny map of a thousand endless rivers that branch and curl up-down-around-and-back. Or like the shadows of windblown vines. Marble is limestone rock. Some of its patterns are made by minerals in the rock and some by fossils-what’s left of plants and animals that lived millions of years ago.
Look for marble the next time you go into a big building downtown. You will see that marble is used for fancy pillars or walls-places where it will be seen. It’s hard to remove marble from the ground, buy you’ll be surprised how easy it is to make paper that has patterns as pretty as those in marble.
You need only four things: a large pan , water, a sheet of paper slightly smaller than the pan and India ink or oil based paint. Fill the pan half full of water. Very slowly dribble a few drops of the ink or paint on the surface of the water.(Do not mix!). Blow lightly over the surface of the water so that the colored drops form a design or pattern. Place the paper flat on top of the water. Pick it up immediately and set it aside-colored side up-to dry.
You can use this marble patterned paper to decorate a wall in your room. You can use it for gift wrappings. Or you can paste it on ordinary little boxes. The marble patterned paper will make the box pretty enough to be placed on a shelf, where they’ll make handy containers for pins, keys, coins and other small things.
With a rumble and a grumble the concrete mixer truck goes along the highway. As the truck moves, its funny looking back part keeps rolling over and over mixing the concrete that is inside. Finally the truck stops at a place where a new road is being made. The concrete comes out of the truck and workmen spread it out evenly on the ground. You’ve probably seen concrete mixer trucks-and perhaps you have a toy one.
The first concrete wasn’t much like the kind we make today. People mixed wet clay with stones from the earth to build walls and houses. It worked- but only in dry countries where the rain couldn’t was it away. And even there it didn’t work nearly as well as today’s concrete.
Concrete can be mixed by hand when it’s to be used for very small jobs, such as replacing one cracked square in a sidewalk. Sand or gravel is mixed together with a heavy gray powder called cement. They are mixed in a box with water. Then everything is stirred around with a shovel or hoe until the mixture looks like gray sticky paste. Lat of all, the mixture is poured into the hole where the new square will be, and the concrete is smoothed out.
Does it sound simple? It is. You could even make your own concrete. All you need is some sand or gravel and some cement from a store. Mix them carefully with water and you will have concrete. Don’t let anything stick to it while it is drying. After it is dry and hard, you can’t make it soft again. Of course for floors and sidewalks and roads and big buildings and bridges it would take too long to mix concrete by hand. So the trucks with built in mixers are used. The mixers do all the work on the way to the job where the concrete is to be used.
Big buildings used to be built with rock or with bricks. Some still are but most big buildings today are built with steel and concrete. Some buildings are made almost entirely of concrete. The concrete is brought by the cement mixer trucks and poured into wood or metal forms to make the walls and floors.(The forms are a little like big low boxes, open at the top.) When the concrete has hardened the forms are taken away-leaving a new concrete wall or floor.
Sometimes parts of a building are made in a factory where concrete is poured into special forms or molds. When the concrete has hardened into the shape that is wanted it is carried to the building in a truck. There it is lifted into place as you might move building blocks into place, except that the concrete is so heavy it has to be lifted with a giant crane. Think about it for a moment. Concrete is almost like a rock-a rock that we can make. We can make this rock into almost any size and shape and build things with it.
In the very long ago times when people lived in caves, they didn’t have many of the things that we have now. They didn’t have hammers and saws. They didn’t have knives. They didn’t have furniture or dishes or blackboards or chalks. They didn’t even have door. But do you know what they did have?Rocks.
They used rocks for just about everything. Maybe the first thing they used rocks for was a chair. They could find a rock chair almost everywhere. It probably didn’t take them long to learn how to throw a rock, either. If a growling wild animal came running at a caveman, about all he could do was run or climb a tree..or pick up a rock and throw it at the animal.
At night a caveman could roll a big rock in front of his cave to keep the wild animals out. Later he learned to use rocks for tools and weapons. Using a hard rock for a hammer he made arrowhead and spearheads out of other rocks. Here’s how he did it” First, he had to find out what kind of rocks would shatter when hit by another rock. A quick and careful blow from a rock hammer would slice a thin layer from such rocks. The caveman kept hitting the thin layer until he had made a point on one end.
With the rock tools he made for himself, the caveman skinned animals, cut meat and sharpened sticks he used for hunting. Another stone that would bot break easily was pounded until it had a sharp edge like an ax. But the caveman’s rock ax didn’t have a handle. He held the stone in his hands and split wood with it. And he used it to dig for roots that were good to eat.
The caveman also used rocks for making pictures. Perhaps he got idea from seeing marks made by bear claws on a cave wall or from the hand prints that he made when he leaned against soft clay. He began to scratch out pictures on the walls of caves. In different places in the world we can still see some of those pictures. And today although we don’t have to live in caves, we still have many the same needs that people had then. And some of the tools we use have not changed much since the caveman first picked up his rocks.